A pulse communication technology exists as one system of communication technology. In the pulse communication technology, system performance depends on how a pulse signal is generated. To make a pulse signal a signal having a component only of any desired frequency band, a method of limiting the frequency band of a pulse signal through a filter and extracting a specific frequency component, a method of intermittently operating an oscillator by a pulse-like control signal, and a method of inputting a pulse-like control signal to a mixer and curtaining a carrier signal, thereby generating a pulse signal exist.
For the pulse generators, required performance includes a short pulse property and a high on/off ratio. The short pulse property contributes to communication speed improvement in communications using a pulse signal. The high on/off ratio contributes to communication quality improvement in communications using a pulse signal.
FIG. 12 shows the block configuration of a related art concerning a short pulse generator using a mixer. FIG. 13 is a timing chart of signal waveforms in FIG. 12. The related art will be discussed below with FIGS. 12 and 13.
A signal 1301 output from an oscillator 1201 is input to a mixer 1203. On the other hand, a control signal 1302 output from a control signal generator 1202 is also input to the mixer. The signal 1301 is curtained by the control signal 1302 and is output from the mixer 1203 as a pulse signal 1303. The circuit configuration is very simple and does not involve a circuit delay element and is excellent in the viewpoint of the short pulse property. However, the signal from the oscillator 1201 leaks when it is off and thus there is a problem in that the on/off ratio is low (refer to Non-patent Document 1).
On the other hand, a circuit for realizing a high on/off ratio by intermittently operating an oscillator as shown in FIG. 14 is proposed. FIG. 15 is a timing chart of signal waveforms in FIG. 14. The related art will be discussed below with FIGS. 14 and 15:
An oscillator 1401 is intermittently operated by a pulse-like control signal 1501 output from a control signal generator 1202 and generates a pulse signal 1502 corresponding to an on interval at which the voltage level is high. At an off interval, the oscillator 1401 does not operate and thus a signal does not leak and a high on/off ratio can be realized. However, the transient characteristic of the pulse signal 1501 is degraded because of operation delay at the operation start time of the oscillator and it is difficult to ensure a good short pulse property (refer to Patent Document 1).
In the related arts shown above, the circuit configuration satisfying demands for the short pulse property and the high on/off ratio at the same time is not provided. In the related art using the mixer (FIG. 12, FIG. 13), it is difficult to realize a high on/off ratio. In the related art using the intermittent oscillator (Non-patent Document 1), it is difficult to ensure a good short pulse property. As a method of solving the two problems, an intermittent multiplication technique of generating a pulse signal by intermittently operating a multiplier exists.
In the intermittent multiplication technique, the multiplier is directly controlled by a control signal and is intermittently operated, whereby high on/off ratio is realized. A pulse generator using the intermittent multiplication technique includes an oscillator, an intermittent multiplier and a filter. A continuous signal generated by the oscillator is input to the intermittent multiplier. the continuous signal and a pulse like control signal having an on interval at which the voltage level is high and an off interval at which the voltage level is low are input to the intermittent multiplier. The intermittent multiplier intermittently operates by a control signal. The circuit operates at the on interval, whereby a harmonic is generated and the circuit does not operate at the off interval, whereby harmonic generation is suppressed. The continuous signal leaking at the off interval is removed through the filter provided at the later stage of the intermittent multiplier and a pulse signal is obtained as an output signal. Accordingly, compatibility between the short pulse property and the high on/off ratio is made possible. Thus, in the intermittent multiplication technique, the oscillator is provided with the oscillation function and the intermittent multiplier is provided with the modulation function and the multiplication function, whereby pulse communications can be realized according to the simple configuration.
On the other hand, as another system of communication technology, frequency modulation communication technology exists. In the pulse communications, data is superposed on amplitude change; while, in frequency modulation communications, a data signal is superposed on frequency change for communications. Usually, to realize frequency modulation communications, a circuit for performing quadrature modulation is formed, but there is a disadvantage in that the circuit configuration is complicated. As a technique for compensating for the disadvantage, VCO (Voltage Controlled Oscillator) modulation technique exists. FIG. 16 shows the circuit configuration to perform VCO modulation and FIG. 17 shows signal waveforms in VCO modulation. A control signal 1702 output from a control signal generator 1602 is input to a control signal terminal (hereinafter, Vt terminal) of a VCO 1601 and oscillation frequency is changed by the control signal 1702, whereby frequency modulation is performed. The frequency of the frequency-modulated signal 1701 is multiplied in a multiplier 1603 at the later stage and an output signal 1703 is output from an output terminal 1604. Thus, in the VCO modulation technique, the VCO is provided with the oscillation function and the modulation function and the multiplier is provided with the multiplication function, whereby frequency modulation communications can be realized according to the simple configuration.
Non-patent Document 1: R. F. Forsythe, “A coherent solid sate, 225 GHz receiver,” Microwave journal, pp. 64-71 1982
Patent Document 1: JP-A-2003-513501